Antivirals are effective in the prophylaxis and therapy of influenza and are likely to be active against a new pandemic variant. They can be divided into the M2 inhibitors, amantadine and rimantadine, and the neuraminidase inhibitors (NIs), zanamivir and oseltamivir. The former are limited in activity to type A viruses, while the latter are also active against type B viruses. Both classes of drugs are approximately 70-90% efficacious when used as prophylaxis. However, the use of M2 inhibitors in therapy is frequently limited by side effects, more common with amantadine, by the emergence of antiviral resistance and by the lack of demonstrated prevention of complications. In contrast, the NIs are better tolerated, antiviral resistance has not emerged as a significant problem and limited evidence suggests they may reduce the frequency of influenza complications. Antiviral agents have not been widely used for either prophylaxis or treatment of annual influenza epidemics. During the early months of the next pandemic they will be the only specific agents that could be used for prevention and treatment. Their availability will depend entirely on the creation of stockpiles of these agents well in advance of the arrival of the pandemic.